In the field of electronic packages, in particular in case that a plastic body encapsulates the chip of the electronic package, carriers or lead frames are widely used. For example, such a lead frame is a metal frame that includes the leads of a plastic encapsulated dual-in-line plastic package. In particular, electronic packages are featured with connection leads penetrating the plastic body surface. Electronic connection from chips of the electronic package to those leads is done by gold (Au) or aluminum (Al) bondwires. In many cases the bondwire is attached to the lead by thermocompression bonding. The inner part is encapsulated by mould compound (EMC). The lead frame holds the leads in place prior to encapsulation and is cut away after encapsulation.
A known problem is the risk of wire bond breakage from the die-pad. Such a wire bond, also referred to as “downbond” is usually made to create an electrical connection from the die surface to the die-pad, which generally forms an electrical ground. Such a downbond has a high risk to come loose from the die-pad when it is used in the final application or during reliability tests.
The die-pad on which the downbond is placed is usually silver-plated to allow wirebonding. The silver-plated surface has a poor adhesion to the moulded compound as used in semiconductor packaging. The die is generally glued on the die-pad, which is a part of the leadframe. The glue-fillet has bad adhesion to the moulding compound, so that during temperature cycling thermo-mechanical stress will cause delamination between moulding compound and leadframe on those locations where adhesion is inferior. The forces driving this delamination increase as the delaminated area grows bigger. The gap height in the delaminated area increases for larger delaminated areas. The delamination and a corresponding gap at the location of the downbond may crack or tear off the bondwire from the die-pad. This will result in electrical failure or performance out of electrical specification.